A mutation (sdr-102) which confers upon the mutant cell the capability of continuous initiation of DNA replication in the absence of protein synthesis (Stable DNA Replication--SDR) has been mapped at 4.6 minutes on the E. coli chromosome map. The SDR is temperature sensitive in a recA200 sdr-102 double mutant. F plasmid replication ceases within a few minutes after the addition of chloramphenical despite the continuous replication of bacterial DNA under such conditions. Attempts are being made to isolate F plasmid replication mutants capable of SDR.